GB523057A - Improvements in telephone and like electric signalling systems - Google Patents

Abstract

523,057. Multi-station public address systems; direct-call telephone systems. DEHN, F. B. (Guided Radio Corporation). Nov. 24, 1938, No. 34246. [Class 40 (iv) ] In a telephone or public address system the transmitting station is connected to one or more receiving stations over two earth-return circuits simultaneously by a pair of transformers at each end and the line windings of these transformers are shunted by resistances or are arranged to be short-circuited on the occurrence of a break in the associated transmission wire. Two way systems; supervisory arrangements. In one arrangement, Fig. 1, in which the transformer line windings are bridged by resistances 11 ... 14, the instrument at one end is connectible at will to the input or output side of an amplifier, the other side being connected to the instrument windings of the transformers. Preferably corresponding points on the lines are at the same potential. In a modification, Fig. 2, means are provided for signalling the occurrence of ground faults and disconnections and for shunting the line windings of the transformers associated with a broken line to reduce the impedance of the instrument windings. The system is set in action by the manual operation of relay contacts 16, 17 which are then held by the energization of relays 11, 12 in series with relays 13, 14 at the other end of the line. If either line wire develops a ground fault the potential of the point to which relay 18 is connected is changed and the relay lights lamp 20. If either line is broken, relays 11 to 14 fall back and relay 25 or 26 pulls up over the other line in series with 13 or 14. Lamp 37 is thus lit and the line windings corresponding to the broken line are short-circuited. Similar arrangements may be provided in one-way systems. One-way systems. As shown in Fig. 3, the transformers are wound so that the transmission wires are at the same potential. All the loud-speakers are coupled to the line between two shunts provided by pairs of resistances 46, 47 and 48, 49. In a modification Fig. 4 (not shown) in which a single transmitter with the aid of two or more transformers in series feeds two or more systems of the kind shown in the other Figure, means are provided for grounding both wires of a, pair to disable groups of loudspeaker stations at will.